An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit which communicates with a fixed base station that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the base station. When the mobile unit moves out of range of one base station, it may connect or “handover” to a new base station and starts communicating with the wired network through the new base station.
In comparison to infrastructure-based wireless networks, an ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of the nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multihopping”) until the packets reach the destination node. As used herein, the term “multihop network” refers to any type of wireless network which employs routing protocols among nodes which are part of a network. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination
The Institute of Electrical and Electronics Engineers (IEEE) 802.16 Working Group on Broadband Wireless Access Standards aims to prepare formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. Among other things, the 802.16 standards define a point-to-multipoint (PMP) system with one hop links between a base station (BS) and a subscriber station (SS). Such network topologies sometimes include pockets of poor-coverage areas. While such coverage voids can be avoided by deploying base stations tightly, this drastically increases both the capital expenditure (CAPEX) and operational expenditure (OPEX) for the network deployment. A cheaper solution is to deploy relay stations (RSs) (also known as relays or repeaters) in the areas with poor coverage. These relay stations can repeat transmissions from the base station so that subscriber stations within communication range of a relay station can continue to communicate with the base station using high data rate links. The incorporation of relay stations in an IEEE 802.16 network transforms it into a multihop network with each node having one or more options to access a network, such as the Internet, via a base station (BS).
For example, networks which comply with the IEEE 802.16j specifications will employ relay stations in an IEEE 802.16e network to provide for range extension and capacity improvements. Depending upon the particular network configuration, a particular subscriber station may gain network access via one or more neighbor relay stations and/or one or more neighbor base stations. In addition, relay stations themselves can have one or more available path options to connect to a particular base station.
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